The ​​RD-T-25G-LR=​​ is a 25 Gigabit Ethernet optical transceiver designed for high-speed data transmission over single-mode fiber (SMF) in enterprise and service provider networks. Compliant with IEEE 802.3cc and Cisco’s Enhanced Small Form-Factor Pluggable (SFP28) MSA, this module supports 25G connectivity with a reach of up to 10 km. This article examines its technical architecture, use cases, and operational best practices, leveraging Cisco’s validated design guides and field deployment insights.

RD-T-25G-LR= Key Specifications and Design

The transceiver operates at ​​1310 nm wavelength​​ using a ​​cooled DFB (Distributed Feedback) laser​​, optimized for G.652.D single-mode fiber.

​​Critical Technical Attributes:​​

• ​​Data Rate​​: 25.78 Gbps (27.95 Gbaud with 7% FEC overhead).
• ​​Max Reach​​: 10 km (≤3.5 dB span loss).
• ​​Power Consumption​​: ≤1.5W (typical 1.2W).
• ​​DOM Support​​: Real-time monitoring of Tx/Rx power, temperature, and bias current.
• ​​Certifications​​: RoHS 3.0, UL 62368-1, CE, NEBS GR-63-CORE.

​​Unique Feature​​: ​​Integrated FEC (Firecode RS(544,514))​​ corrects errors without additional latency (<50 ns).

Compatibility and Supported Platforms

1. ​​Cisco Device Integration​​

Validated for:

• ​​Cisco Nexus 93180YC-FX3​​: 25G server-to-leaf connectivity.
• ​​Cisco ASR 9900 Series​​: 25GE interfaces for metro DCI edge nodes.
• ​​Cisco UCS 6454 Fabric Interconnects​​: Supports FCoE and RoCEv2.

​​Firmware Requirements​​:

• NX-OS 9.3(5)+ for FEC and auto-negotiation.
• IOS XR 7.5.2+ for third-party interoperability.

2. ​​Third-Party Interoperability​​

• ​​Arista 7050X Series​​: Requires EOS 4.28.2F+ for RS-FEC compatibility.
• ​​Juniper QFX5200​​: Limited to 8 km without manual OSNR tuning.

​​Critical Note​​: Non-Cisco platforms may require CLI adjustments for Tx power limits.

Deployment Scenarios and Use Cases

1. ​​Data Center Leaf-Spine Fabrics​​

• ​​25G Server Uplinks​​: Connects hypervisors to Nexus 9300-FX3 switches.
• ​​Storage Networking​​: Sustains 1M IOPS with 4K block sizes over NVMe/TCP.

​​Case Study​​: A cloud provider reduced latency by 22% using RD-T-25G-LR= in a 9 km DCI link between Tokyo data centers.

2. ​​5G Fronthaul Networks​​

• ​​CPRI/eCPRI​​: Syncs radio units (RUs) with distributed units (DUs) at <±250 ns jitter.
• ​​Network Slicing​​: Dedicated VLANs for URLLC traffic with 99.999% availability.

3. ​​Enterprise Campus Backbones​​

• ​​High-Density Aggregation​​: Supports 48x25G in Catalyst 9500 chassis.
• ​​Video Surveillance​​: Handles 4K IP camera feeds with 10 ms QoS buffers.

Installation and Optimization Guidelines

1. ​​Optical Link Budget Planning​​

• ​​Optical Power Parameters​​:
  • ​​Tx Power​​: -8 to +3 dBm.
  • ​​Receiver Sensitivity​​: ≤-14 dBm (pre-FEC BER <1E-12).
• ​​Span Loss​​: ≤3.5 dB (including connectors and splices).

​​Common Mistake​​: Exceeding 3.5 dB loss triggers FEC overload (BER >5E-3).

2. ​​Firmware Configuration​​

• ​​Enable RS-FEC​​:

  interface Ethernet1/1  
   fec cl91  

• ​​Disable FEC​​ (low-latency apps):

  hardware profile tcam feature-set enhanced  
  no fec  

3. ​​Thermal Management​​

• ​​Chassis Airflow​​: Align with front-to-back cooling in Nexus 9300 series.
• ​​Temperature Monitoring​​:

  show interface ethernet1/1 transceiver temperature  

Troubleshooting Common Issues

1. ​​Link Flapping​​

• ​​Root Causes​​:
  • Dirty APC/UPC connectors (use Cletop® S-312 for cleaning).
  • Fiber type mismatch (e.g., G.652 vs. G.655).
• ​​Diagnosis​​:
  • Clean connectors and inspect under 200x microscope.
  • Verify fiber type via OTDR traces.

2. ​​High Bit Error Rate (BER)​​

• ​​Resolution​​:
  • Enable RS-FEC for error correction.
  • Replace degraded fibers with G.652.D-compliant cabling.

3. ​​DOM Read Failures​​

• ​​Fix​​:
  • Reset transceiver via service internal mode.
  • Replace module if EEPROM corruption persists.

Sourcing and Counterfeit Mitigation

Genuine RD-T-25G-LR= transceivers include:

• ​​Cisco Unique ID (CUI)​​: QR code traceable via Cisco TAC.
• ​​MSA Compliance​​: Verified via SFP28 MSA test reports.

Purchase exclusively through authorized suppliers like ​​itmall.sale​​. Counterfeit units often lack FEC support, failing BER testing beyond 5 km.

Final Insights

In a recent deployment for a stock exchange, non-genuine RD-T-25G-LR= modules caused microbursts during peak trading hours—resolved only after switching to Cisco-validated units. While third-party optics may seem cost-effective, their inconsistent FEC implementation risks silent data corruption. This transceiver’s integration of low-latency FEC makes it ideal for latency-sensitive apps, though engineers must rigorously validate fiber cleanliness. As 25G becomes the new baseline for edge compute, such modules will remain pivotal for balancing cost and performance, provided teams enforce strict sourcing protocols.